Stuff the box so it will not get crushed. One sheet of crumpled paper from your recylce bin works well. Clearly write the address above on your box and consider using colorful stamps to close the top and bottom. The stamp cancellations showing it's origin will make it even more meaningful.
It's okay to put as many stamps as you want anywhere on your SOUL BOX as long as they add up to the postage due. If you have stuffed the box if will go through the postal system just fine.
Send us a bunch for almost the same cost when mailed Parcel Post!
about 13 SOUL BOXES and a lightweight container